Abstract While daytime heatwaves are well‐known to exacerbate surface ozone (O3) pollution, the role of compound heatwaves with persistent day‐night hot in O3 pollution remains unclear. Taking China’s Sichuan Basin (SCB) as an example, we find compound heatwaves persistently intensify surface O3 concentration day and night, with significant positive anomalies of 29.3 μg/m3 and 12.1 μg/m3 during daytime and nighttime, respectively. In details, daytime hot triggers high daytime O3 concentration by enhancing O3‐forming photochemistry, thereby providing a nocturnal residual layer (RL) with O3‐rich air and substantial heat storage. Nighttime, the persistent day‐night hot combined with easterly flow jointly drive a plateau‐basin secondary circulation across RL and stable boundary layer over the SCB, facilitating RL’s O3‐rich air mixing to the surface and increasing nighttime O3 concentration. These findings advance understanding of how extreme heat and large‐scale topographic forcing jointly modulate atmospheric environmental changes in plateau‐basin regions.

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